Why this error coming in ver13. When click on Email Receipt button in POS Page
File “/home/frappe/frappe-bench/apps/frappe/frappe/core/doctype/communication/email.py”, line 231, in prepare_to_notify
doc.content += get_attach_link(doc, print_format)
TypeError: unsupported operand type(s) for +=: ‘NoneType’ and ‘str’